1. (Field of the Invention)
The present invention relates to a semiconductor integrated circuit device of a surface-mount type which is mounted on one surface of a printed circuit board.
2. (Description of the Prior Art)
In the field of semiconductor integrated circuit devices for use in portable terminal equipment such as portable computers and portable phones, there has been a growing demand for miniaturization. To meet this demand, semiconductor integrated circuit devices make use of a flat package for surface mounting, having narrow lead terminals spaced at a small pitch. Since this design causes the connection between the lead terminals and the electrodes on a substrate such as, for example, a printed circuit board, to be small, the soldering tends to be defective. On the contrary, it has become necessary to further improve the reliability of the connection in point of machine-resistance and heat-resistance because portable terminal equipment is often used outdoors under severe conditions.
Generally, a semiconductor integrated circuit device is composed of a semiconductor integrated circuit chip, a resin-molded package or a ceramic package in which the chip is sealed, and a circuit formed in the chip and adapted to be electrically connected with the lead terminals which are partly embedded in the package. The lead terminals are usually placed side by side along two sides or four sides of the package, thereby connecting the circuit formed in the chip and an external circuit. Those packages where lead terminals are disposed along two sides thereof are called SOP (Small Out-line Package) and those where lead terminals are disposed along four sides thereof are called QFP.(Quad Flat package).
FIG. 15 is a plane view of a conventional SOP type semiconductor integrated circuit device. This device includes a package 2, a semiconductor integrated circuit chip (not shown) completely enclosed in the package 2, and lead terminals 3. The lead terminals 3 are uniform in width and protrude an equal distance from each of the two opposed sides of the package 2.
However, this conventional semiconductor integrated circuit device has a drawback in that the strength of the solder connection between the lead terminals 3 and the electrodes of the packaging substrate is insufficient and lacks reliability. For example, when a reliability test was conducted by mounting the conventional semiconductor integrated circuit device on the printed circuit board, and applying mechanical and thermal stress to the apparatus, the solder connection cracked to become defective. The incidence of the defective tends to increase as the lead terminals are made narrower, which has been a problem in downsizing semiconductor integrated circuit devices.